Linear actuator

ABSTRACT

A linear actuator comprising of two elongate resilient elements (10, 12) joined together at their opposite ends (13, 14), a first one of the elements is fixed at a point intermediate its ends (16) and the two elements (10, 12) are arranged to carry an electric current which causes the two elements (10, 12) to move apart when they are placed in a transverse magnetic field. The linear actuator may be used to control the opening and closing of a valve in a fluid dispensing device, where a needle (20) is attached to the second element (12), which needle co-operates with a valve orifice.

This invention relates to a linear actuator and more particularly to alinear actuator in the form of an electrical transducer which produces alinear displacement when driven by an electric current.

In accordance with this invention there is provided a linear actuatorwhich comprises two elongate resilient elements joined together at theiropposite ends, a first one of the elements being fixed at a pointintermediate its ends and the two elements being arranged to carry anelectric current, and means for providing a magnetic field transverse tothe two elements so that when the electric current is passed throughthem, the two elements move apart.

The two elongate elements may be formed by opposite sides of amulti-turn coil.

The two elongate elements may be disposed in the same transversemagnetic field, or they may be disposed in respective transversemagnetic fields of opposite senses.

When the electric current through the two elongate elements of theactuator is terminated, the two elements return to their rest position(i.e. they move back towards each other) under their own inherentresilience.

It will be appreciated that the actuator produces a linear displacementof an intermediate point on the second element, which is opposite to thefixed point on the first element. The actuator produces a displacementthrough a substantial distance at high speed immediately in response tothe onset and termination of the electric current.

The linear actuator may be used to control the opening and closing of avalve in a fluid dispensing device and for example may include a needleattached to the second element, which needle co-operates with a valveorifice.

Embodiments of this invention will now be described by way of exampleonly and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic side view of one embodiment of linear actuatorcontrolling a needle valve in a fluid dispenser;

FIG. 2 is a section through the actuator of FIG. 1;

FIG. 3 is a schematic side view of a second embodiment of linearactuator-controlling a needle valve in a fluid dispenser; and

FIG. 4 is a section through the actuator of FIG. 3.

Referring to FIGS. 1 and 2 of the drawings, there is shown a linearactuator which comprises a multi-turn flat coil which is provided with acoating to insulate adjacent turns from each other. The coil, beinggenerally flat, thus provides in effect two elongate elements 10, 12having their opposite ends connected together at 13, 14. An intermediateor mid-point of the element 1 is mounted to a fixed support 16 and thetwo ends of the coil are brought out as electrical leads 17, 18. A valveneedle 20 is fixed to the other element 12 at its mid point, and isdirected away from the element 10 and its support 16. As shown in FIG.2, a permanent magnet 22 is provided with its poles either side of thecoil, so as to give a magnetic field which is common to the two elements10, 12 of the coil and is transverse to the plane containing the coil.

In operation, if an electric current is passed through the coil in thedirection shown by the arrows in FIG. 1, it is found that the twoelements 10, 12 move apart, i.e. the element 12 and its needle 20 moveaway from the fixed support 16. The electric current through the element10 situated in the magnetic field from the permanent magnet produces aforce causing this element to move away from its support 16 andtherefore to bend as shown. The bending moment forces are transferred tothe element 12 to cause this also to bend.

Thus both elements 10, 12 bow outwardly away from each other when theelectric current is applied. When the electric current is terminated,the two elements 10, 12 straighten out (therefore the needle 20 movingback towards the fixed support 16) under their inherent resilience.

Referring to FIGS. 3 and 4, there is shown a modified embodiment oflinear actuator, in which the coil is of generally rectangular shapeproviding in effect two elongate elements 10, 12 joined at theiropposite ends by shorter elements 11, 15 so that at rest the elements10, 12 are parallel to each other but spaced apart. The mid-point of theelement 10 is mounted to a fixed support 16 and the end of the coil arebrought out to leads 17, 18 as in FIGS. 1 and 2. A permanent magnet isarranged to provide respective fields of opposite sense for the twoelements 10, 12 of the coil; thus on one side of the coil there is aN-pole adjacent the element 10 and a S-pole adjacent the element 12,whilst on the other side of the coil there is an S-pole adjacent theelement 10 and a N-pole adjacent the element 12.

In operation, when an electric current is passed through the coil in thedirection shown by the arrows in FIG. 3, it is found that the twoelements 10, 12 of the coil move apart i.e. the element 12 and itsneedle 20 move away from the fixed support 16. Thus, the electriccurrent through the element 10 situated in its transverse magnetic fieldproduces a force causing this element to move away from to its support16 and therefore to bend. The electric current through the element 12,situated in its transverse magnetic field of opposite sense, produces aforce also in a direction away from the support 16, so that this element12 also bends The effect is for both elements 10, 12 to bow outwardlyaway from each other and so displace the needle 20 away from the fixedsupport 16. When the electric current is terminated, the elements 10, 12return to their rest positions under their inherent resilience.

In each of the embodiments described, the needle 20 co-operates with avalve orifice 30 or nozzle in the ejection chamber of a fluid dispensingdevice and in particular such that when the electric current is passingthrough the coil the needle is displaced into a position seating withinthe valve orifice so as to close this against fluid flow: when thecurrent is interrupted the needle is displaced away from the valveorifice so as to open this for fluid flow from within the ejectionchamber.

A displacement of the linear actuator in the opposite direction to thatdescribed can be achieved by passing a current through the coil in theopposite direction to that shown. Thus in the case of the fluiddispensing device, an electric current may be passed through the coil inthe direction shown to bow the two elements 10, 12 outwardly relative toeach other and urge the needle against its seat to close the valveorifice: then the valve may be opened by passing a current through thecoil in the opposite direction.

I claim:
 1. A linear actuator which comprise two elongate resilientelements joined together at their opposite ends, a first one of theelements being fixed at a point intermediate its ends and the twoelements being arranged to carry an electric current, and means forproviding a magnetic field transverse to the two elements so that whenthe electric current is passed through them, the two elements moveapart.
 2. A linear actuator as claimed in claim 1 in which the twoelongate elements are formed by opposite sides of a multi-turn coil ofwire.
 3. A linear actuator as claimed in claim 1 in which the twoelongate elements are disposed in the same transverse magnetic field. 4.A linear actuator as claimed in claim 1 in which the two elongateelements are disposed in respective transverse magnetic fields ofopposite senses.
 5. A linear actuator as claimed in claim 1 in which thetwo elongate elements exhibit inherent resilience so that they return totheir rest positions on cessation of electric current flow.
 6. A linearactuator as claimed in claim 1 in which the two elongate elements arespaced apart from each other and joined at their opposite ends byshorter elements.
 7. A linear actuator as claimed in claim 1 which isused to control the opening and closing of a valve in a fluid dispensingdevice.
 8. A linear actuator as claimed in claim 7 in which a needle isattached to the second element, which needle cooperates with a valveorifice.